[0001] The present invention relates to a helicopter rotor of the type substantially comprising
a hub connected to a drive shaft to rotate the rotor; and a number of blades fixed
to and projecting radially from the hub.
[0002] More specifically, each blade extends lengthwise substantially radially, is rotated,
in use, by the hub in a drive plane perpendicular to the axis of the drive shaft,
and is movable in all planes with respect to the hub to manoeuvre the helicopter.
[0003] Established helicopter design criteria require that, for each operating condition
of the helicopter, the work frequencies of the rotor and blades fall within a different
range from that of the natural frequencies of the other component parts of the helicopter.
[0004] If such is not the case, the helicopter may be subjected to particularly severe,
even destructive, vibration.
[0005] In helicopter design, appropriate setting of said natural frequencies is therefore
essential; for which purpose, vibration damping devices are known to be interposed
between the hub and each blade, either inwards or outwards of the blades.
[0006] Location of the damping device outwards of the blades produces additional aerodynamic
drag which impairs performance and consumption of the helicopter.
[0007] To reduce such drag, the damping devices must be made as small as possible. By so
doing, however, the loads acting on the rotor may induce severe stress on, and even
cause detachment of, the damping devices, thus resulting in malfunctioning of the
rotor and possibly additional stress on the helicopter, making it difficult to manoeuvre.
[0008] Moreover, if detached, the damping device may hit the helicopter rotor, with obvious
consequences in terms of safety.
[0009] Conversely, location of the damping device inwards of the blade poses problems caused
by the damping device interacting with the portion of the blade connected to the hub,
and by sliding movements between the contacting parts.
[0010] More specifically, such sliding movements may produce wear and localized heating
of the contacting parts, thus reducing the working life of the parts and dissipating
energy at the expense of the efficiency of the helicopter.
[0011] Location of the damping devices inwards of the blades also poses size problems, making
it necessary at times to redesign the rotor hub.
[0012] It is an object of the present invention to provide a helicopter rotor designed to
eliminate at least some of the aforementioned drawbacks in a straightforward, lowcost
manner.
[0013] According to the present invention, there is provided a helicopter rotor as claimed
in Claim 1.
[0014] A preferred, non-limiting embodiment of the present invention will be described by
way of example with reference to the accompanying drawings, in which:
Figure 1 shows a partial longitudinal section of a helicopter rotor in accordance
with the present invention;
Figures 2 and 3 show smaller-scale sections, along line II-II in Figure 1, of the
rotor in two different operating conditions.
[0015] Number 1 in the accompanying drawings indicates as a whole a rotor, for a helicopter
(not shown), substantially comprising a hub 2 of axis A; a number of blades 3 (only
one shown in detail) projecting substantially radially from hub 2; and a number of
damping devices 4 (only one shown in detail), each interposed between a respective
blade 3 and hub 2 to reduce the vibration induced on the helicopter by rotor 1.
[0016] More specifically, hub 2 comprises a radially inner cylindrical body 5, of axis A,
for housing a drive shaft 6 of rotor 1; and a radially outer tubular portion 7 having
a curved polygonal profile and connected to cylindrical body 5 by a number of angularly
equally spaced radial spokes 8.
[0017] In other words, hub 2 comprises a number of through seats 9, of axis A, equally spaced
about axis A and by which to attach respective blades 3.
[0018] More specifically, each seat 9 is bounded circumferentially by two adjacent spokes
8, and radially by cylindrical body 5 and tubular portion 7.
[0019] As shown in the accompanying drawings, each blade 3 extends predominantly in a direction
C substantially radial with respect to axis A, and comprises a main body 10 (shown
only partly in the accompanying drawings) defining the helicopter lift/flight surfaces;
and a coupling member 11 bolted to a radially inner end of main body 10 to connect
blade 3 to hub 2.
[0020] More specifically, coupling member 11 of each blade 3 is substantially C-shaped,
and comprises two parallel arms 12, between which the radially inner end of main body
10 of blade 3 is fixed; and a connecting portion 13 connecting arms 12 and which engages
a respective seat 9 of hub 2.
[0021] More specifically, connecting portion 13 of coupling member 11 of each blade 3 engages
a respective seat 9 of hub 2 with the interposition of a bearing 15 allowing blade
3 to move in all possible planes in space about a centre of rotation R.
[0022] More specifically, each bearing 15 is housed between a convex circumferential projection
16 formed on tubular portion 7 of hub 2 at relative seat 9, and a concave recess 17
complementary in shape and formed on connecting portion 13 of coupling member 11 of
relative blade 3.
[0023] As shown clearly in the accompanying drawings, each projection 16 on tubular portion
7 of hub 2 faces axis A, while each recess 17 is formed on the side of connecting
portion 13 of relative blade 3 facing away from axis A.
[0024] Given the construction arrangement described above, each blade 3 can be rotated integrally
with hub 2 in a plane perpendicular to axis A, and is movable with respect to hub
2 about centre of rotation R.
[0025] More specifically, of all the possible movements of each blade 3, the most significant,
for a clear understanding of the present invention, is that about an axis B extending
through centre of rotation R and perpendicular to axis A and direction C. The other
known possible movements of blades 3 are not described for the sake of simplicity.
[0026] As shown in Figures 2 and 3, each damping device 4 is housed between arms 12 of coupling
member 11 of relative blade 3, and is secured, on one side, to arms 12, and, on the
opposite side, to tubular portion 7 of hub 2.
[0027] More specifically, each damping device 4 is enclosed between arms 12 in a direction
parallel to axis A, and is enclosed radially between tubular portion 7 of hub 2 and
the radially inner end of main body 10 of relative blade 3. In other words, each coupling
member 11 defines a frame-like portion, of relative blade 3, in turn defining a seat
18 open in a direction parallel to axis B and for housing a relative damping device
4.
[0028] Each damping device 4 advantageously comprises a plate member 20, the radially inner
end 21 of which, with respect to axis A, is fixed to tubular portion 7 of hub 2, and
the radially outer end 22 of which, with respect to axis A, is secured to arms 12
of coupling member 11 of relative blade 3 by means of a connecting member 23 made
partly of elastic material.
[0029] More specifically, plate member 20 is V-shaped, lies in a plane parallel to arms
12 of coupling member 11 of relative blade 3, and is symmetrical with respect to direction
C.
[0030] More specifically, plate member 20 comprises a tip portion 24, from which originate
two diverging lateral branches 25.
[0031] Tip portion 24 defines end 22 of plate member 20, while the free ends of lateral
branches 25 together define end 21 connecting plate member 20 to tubular portion 7
of hub 2.
[0032] Tip portion 24 of plate member 20 has an end ball 26 connected to connecting member
23 to define an articulated joint as explained in detail later on.
[0033] More specifically, connecting member 23 comprises a parallelepiped-shaped supporting
member 27 fixed between the free ends of arms 12, with the interposition of respective
pads 28 of elastomeric material, and defining a spherical seat 30 for housing ball
26 of plate member 20 with the interposition of a bearing 29 also made of elastomeric
material.
[0034] As shown particularly in Figure 1, lateral branches 25 are fixed peripherally to
tubular portion 7 of hub 2, and define, together with tip portion 24, a cavity for
receiving part of tubular portion 7; which construction arrangement provides for limiting
the overall size of rotor 1 radially with respect to axis A.
[0035] An important characteristic of the present invention is that, during movement of
relative blade 3, plate member 20 is flexible about an axis D coaxial with axis B.
[0036] Axes D and B being coaxial, no sliding movements occur, as each blade 3 rotates about
axis B, between relative plate member 20 and the parts connecting plate member 20
to hub 2 and blade 3, thus drastically reducing wear and localized heating.
[0037] In an alternative embodiment not shown, the same results may also be achieved with
axis D located close to and parallel to axis B. More specifically, axis D may be located
at a distance from axis B equal to no more than 10%, and preferably within 5%, of
the total length of plate member 20 in direction C.
[0038] Further advantages of rotor 1 as described and illustrated herein are indicated below.
[0039] In particular, being V-shaped, each plate member 20 is far more resistant to bending
moments operating in a plane defined by axis A and relative direction C, and to shear
forces perpendicular to direction C.
[0040] In fact, each plate member 20 has a cross section, crosswise to the plane of plate
member 20, characterized by decreasing in area and moment of inertia from axis A towards
relative connecting member 23.
[0041] The resistance of plate member 20 to said bending moments is therefore optimized,
by the sections close to axis D, and therefore subjected to greater stress by the
bending loads on blade 3, having a greater moment of inertia.
[0042] Similarly, close to axis A, the resistance of plate member 20 to shear stress is
improved, by plate member 20 having larger-area sections close to axis A.
[0043] Each damping device 4 is therefore characterized by being smaller in overall size
radially with respect to axis A, and by improved resistance to external stress as
compared with known solutions.
[0044] Moreover, if detached accidentally from rotor 1, each damping device 4 remains inside
relative seat 18, and is prevented from escaping from relative blade 3 and possibly
colliding with rotor 1.
[0045] In other words, in the above conditions, malfunctioning of rotor 1 and additional
stress on the helicopter are therefore reduced.
[0046] Finally, housing each damping device 4 inside a closed seat 18 defined by relative
blade 3 produces no additional aerodynamic drag, thus improving performance and consumption
of the helicopter.
[0047] Clearly, changes may be made to rotor 1 as described and illustrated herein without,
however, departing from the scope defined by the accompanying Claims.
1. A rotor (1) for a helicopter, comprising:
- a hub (2) rotating about a first axis (A);
- a number of blades (3) projecting from said hub (2) in respective longitudinal directions
(C) lying in a plane crosswise to said first axis (A), each said blade (3) being connected
to said hub (2) so as to be movable at least about a second axis (B) crosswise to
said first axis (A) and to the relative said longitudinal direction (C); and
- a number of damping devices (4) for damping vibration of said helicopter, and each
interposed between a respective said blade (3) and said hub (2);
characterized in that each said damping device (4) comprises a plate member (20) fixed, on one side, to
said hub (2), and connected, on the opposite side, to the relative said blade (3)
by elastic means (26, 27, 28, 29); and in that said plate member (20), during movement of said blade (3), is flexible about a third
axis (D) parallel to said second axis (B) and located close to the second axis (B).
2. A rotor as claimed in Claim 1, characterized in that said third axis (D) is coaxial with said second axis (B).
3. A rotor as claimed in Claim 1 or 2, characterized in that said plate member (20) is connected to said elastic means (28, 29) by an articulated
connection (26, 27) .
4. A rotor as claimed in any one of the foregoing Claims, characterized in that said plate member (20) is V-shaped, the tip (24) of which is connected to the relative
said blade (3), and the end (21) of which, opposite said tip (24), is connected to
said hub (2).
5. A rotor as claimed in Claim 4, characterized in that said plate member (20) is fixed peripherally to said hub (2), and defines a cavity
for receiving part of the hub (2).
6. A rotor as claimed in any one of the foregoing Claims, characterized in that each said blade (3) comprises, close to said hub (2), a frame-like portion (11) defining
a seat (18) for housing a relative said damping device (4).
Amended claims in accordance with Rule 86(2) EPC.
1. A rotor (1) for a helicopter, comprising:
- a hub (2) rotating about a first axis (A);
- a number of blades (3) projecting from said hub (2) in respective longitudinal directions
(C) lying in a plane crosswise to said first axis (A), each said blade (3) being connected
to said hub (2) so as to be movable at least about a second axis (B) crosswise to
said first axis (A) and to the relative said longitudinal direction (C); and
- a number of damping devices (4) for damping vibration of said helicopter, and each
interposed between a respective said blade (3) and said hub (2);
characterized in that each said damping device (4) comprises a separate plate member (20) fixed, on one
side, to said hub (2), and connected, on the opposite side, to the relative said blade
(3) by elastic means (26, 27, 28, 29); and
in that said plate member (20), during movement of said blade (3), is flexible about a third
axis (D) parallel to said second axis (B) and located close to the second axis (B)
.
2. A rotor as claimed in Claim 1, characterized in that said third axis (D) is coaxial with said second axis (B).
3. A rotor as claimed in Claim 1 or 2, characterized in that said plate member (20) is connected to said elastic means (28, 29) by an articulated
connection (26,